1. Technical Field of the Invention
The invention relates to an apparatus and method for printing image information having a specific orientation on sheets of a receiving material. More particularly, this invention relates to a method and apparatus for printing two images on a receiving material with a printer which rotates at least one of the images with a rotation method that utilizes minimal memory space to rotate images. The invention also relates to a method and apparatus for rotating a series of images to position pairs of images from the image series in a specific orientation on a corresponding series of receiving materials.
2. Description of Related Art
In general, printing two images having an identical orientation on a single sheet is known. For example, U.S. Pat. No. 4,763,167 describes a copying method in which the image information from two different original sheets is read or scanned successively and, after storage and processing, is printed on one copy sheet such that the reading orientations of the two images are identical and are perpendicular to the long side of the copy sheet. With this conventional method, it is possible to obtain copy sheets which may be folded in the middle, between the images, in order to form a folded sheet as shown in the '167 patent. A plurality of such copy sheets may be assembled to create a manual or booklet.
According to another known method of reproduction, original images are printed twice on one copy sheet and then the copy sheet is cut through between the two (identical) images, thus giving one page for each of two booklets, e.g. manuals, to be produced.
Alternatively, instead of a booklet with a fold line, spine, or some other binding portion at the center of the sheet, it is possible to utilize a binding portion provided at the left-hand or right-hand (short side) of the copy sheets. To print on sheets provided with such alternative binding portions, two images are typically read out of an image or page memory with a 0.degree. or 180.degree. rotation and then printed on the sheet accordingly.
Increasingly, when images from original sheets are reproduced, copy sheets which may or may not be completely adapted to the method of subsequent collation are being used. For example, copy sheets provided with a binding portion on two short sides such as perforations suitable for storage in a ring binder are often used to reproduce images. Such copy sheets, which may or may not be connected in continuous form, are typically cut in half at a perforation leaving two half-sheets each of which includes a binding portion on a short side thereof. If the above-described conventional methods of reproduction are used with such copy sheets, identical pages would be obtained after cutting through the sheet, but the perforated edges would be at opposite sides, something which is quite unacceptable.
Furthermore, if two different pages, e.g. two consecutive pages, are imaged on copy sheets provided with a binding portion on two short sides, it would be a complex matter to collate the booklets, because when the copy sheet is cut through the center the pages would have to be arranged alternately.
Also, in conventional duplex printing, the image of the first original is printed on one side of the copy sheet and then the copy sheet is flipped 180.degree. about the short axis and then the image of the second information sheet is printed on the second side of the copy sheet. In this case, action must be taken to keep the image orientation the same on both sides of the copy sheet.
An example of conventional duplex printing is described in Applicants' commonly assigned European Patent Application 0 628 922. According to the method known therefrom, optimal use is made of the memory space by storing the image data of the first original image in ascending address sequence in the memory starting from the first free memory address, but storing the image data of the second original image in reverse address sequence in the memory starting from the last free memory address. On read-out, the image data are always read out of the memory in ascending address sequence, so that the image data of the second original image are fed to the printer with an automatic 180.degree. rotation.
Furthermore, conventional image rotation typically writes the data of an image line-by-line into a bit map memory and then reads out the data column-by-column (from bottom to top) from the memory. After the read-out is completed and the memory is empty, the data of the next image to be rotated can then be written into the memory. In other words, before the data of each subsequent image can be written into the memory it is necessary to wait until the read-out of the preceding image is completed.
To remedy the delay caused by this conventional rotation method, it is known to utilize two memories which are used alternately: while one image is being read out of the first memory, the next image is being written into the second memory. However, this conventional remedy increases the cost and complexity of the resultant system.
Furthermore, it should be noted that a method of writing image data from an image within a series of images into a memory at memory locations that have been freed by reading out the preceding image in the series is described in U.S. Pat. No. 5,151,976. The '976 patent writes an image into a memory line-by-line and then reads-out this image in a fixed, sawtooth pattern to rotate the image through 90.degree. plus a reflection. Because of the limitations on the rotation angle, the fixed, sawtooth addressing formula described in the '976 patent is therefore not suitable rotating images as intended by the present invention, nor is it suitable for changing the angle of rotation for each image optionally in a series of images.